Working on my friends 69 Elky. Ive got a 12v draw that only goes away when the red wire is disconnected from the alternator. I had the regulator, horn relay, and even the bulkhead connector disconnected. Can an alternator have a short in it like that? o No: Im skeptical because I never had an alternator do this. Im going to bring it to another buddies auto electric shop in the area to bench test it tomorrow.
wait regulator was unplugged... my bad. not sureexternal regulator? alt hasnt been converted to internal has it?
External regulator still in place. Yes, it was disconnected. That was the first thing I went for. Ive seen plenty of those that have gone bad
The insulated post at the casing, the diodes, or the windings, could have failed. There are a nubmer of things that go wrong with alternators that will kill batteries. Best advice is check it out with an Ohmmeter if you are up to it, or just pull it and take it to NAPA or AutoZone to be tested.
Yes I have seen alternators short out internaly. Not that common, but it does happen. I am sure that is whats wrong with this car.
Jason,if you touch the battery wire to the alternator post & get a spark of any kind the alternator is bad.
Happened to me once, what is your voltage reading when you run? If a diode is broke the rectifying no longer works properly, and the alternator is putting out DC boosted with part AC. When one of my diodes was shot I could read 18V on the battery terminals with a normal cheap volt meter in DC mode. Battery water was boiling, all lamps was shining real strong and battery was emptied if I didn't drive daily.
Jaime, thanks for chiming in:beers2: I'd be interested in hearing your thoughts about my exchange today between my friend and the rebuilder. Looks like the alternator was the culprit. So I told my buddy the price I was quoted for the reman alternator. He was floored. He said "I can get one from the local auto parts store for $40" What makes his worth $125??" The rebuilder said if my friend wants a $40 alternator, he can build him one no problem. He said the difference is the components. The US made front case bearing for example, cost him $15 alone. He could easily get a Chinese bearing for 79 cents and use that but he doesnt. Most of the rotors you find in the cheapo alternators are aftermarket and use copper clad aluminum windings. he uses copper windings on original Delco cores. The cases are refinshed to give them a more factory appearance. There dont look like a typical alternator finish. I forgot what he said exactly, but his looks like original GM. The auto parts store alternator has a rough bead blasted look. In fact, the one I brought in was blasted so hard that the original stampings were almost worn away. His are more of a darker gray. And the numbers on the case he provided still looked sharp. I think he might use a tumbler maybe? o No: When I dropped it off, the front case wasnt period correct. the top ear was sliighty different. he found a case with the correct serial number for a 69 Chevelle. He also used a gold cad plated fan and a thick style pulley, not the stamped steel pulley that was on there As an FYI, his auto parts store alternator lasted him 5 years but it was probably only 2000 miles.
I've got a massive 12v draw! If you don't like sparks, you could put a 12V test light between the battery + and the alternator output stud (other wires removed). Any light means bad alternator diodes. Bruce Roe
Re: I've got a massive 12v draw! Im still a little confused on this. With the negative cable removed and a meter installed in between the terminal and battery, what should a meter read? 12v or zero?
Re: I've got a massive 12v draw! With the negative cable removed would have to read zero---battery is not in the circuit. John
Re: I've got a massive 12v draw! There is no "circuit" if the negative cable is off the battery and you are measuring between the positive terminal of the battery and the alternator.
Re: I've got a massive 12v draw! I just re-read my post. I dont think I was clear. What Im doing is removing the negative cable (positive still attached) and putting a meter in between the negative terminal of the battery and the cable. Im getting a reading of 12v.
Re: I've got a massive 12v draw! OK, my misunderstanding! Should read zero. Most likely a bad diode in the alternator if you read 12V.
Re: I've got a massive 12v draw! Just an update for you guys- Replaced the alternator with a remanufactured from the local rebuilder. We dropped off the brand new regulator to get adjusted and tested. He ran the alternator and regulator for 2 hourrs on the bench. We put it into the car and ran it around town. It was fine for a 1/2 hour- rock steady at 14.5 volts on the voltmeter. We went to restart it and the alt light came on. The alternator is making a wierd whining noise now. We rechecked and it looks like the diodes in the new alternator are blown. We opted to get a new Delco regulator and chuck the Standard brand regulator. We have the alternator back out and we're going to drop both pieces back off at the rebuilder. Whats going on here? Im starting to go insane. Seemed like a pretty straight forward job when I started...
